I. Field of the Invention
The present invention relates generally to position sensors and, more particularly, to an inductive position sensor.
II. Description of Related Art
In automotive vehicles, the throttle pedal has traditionally been mechanically connected to the engine throttle by a cable. However, in more modern vehicles a throttle position sensor is mechanically connected to the pedal and generates an electrical output signal indicative of the position of the throttle pedal which varies as the throttle pedal is depressed by the driver. Such systems are sometimes referred to as “fly by wire” systems.
In one type of previously known throttle position sensor, the sensor includes a circularly wound transmitter coil typically formed on a printed circuit board. This transmitter coil is excited by high frequency alternating source so that the transmitter coil generates electromagnetic radiation. Even though the transmitter coil is usually arranged in a circular pattern, other pattern configurations may alternatively be used.
A receiver coil is also formed on the printed circuit board in close proximity to the transmitter coil. This receiver coil receives electromagnetic radiation from the transmitter coil through inductive coupling and generates an output signal as a result of the signal received from the transmitter coil.
Unlike the transmitter coil, however, the receiver coil includes a first loop and a second loop that are wound in the opposite direction when viewed in plan. Consequently, the inductive coupling between the transmitter coil and the first loop of the receiver coil generates a voltage opposite in polarity from the inductive coupling between the transmitter coil and the second loop of the transmitter coil. The receiver output is then a combination or sum of the signals from the first and second loops of the transmitter coil which are connected in series with each other.
In order to generate an output signal representative of the position of the throttle, a coupler element is rotatably mounted within the throttle position sensor and rotates in synchronism with the depression and release of the throttle pedal. This coupler element, furthermore, is constructed of a conductive material, such as metal, which cancels magnetic flux received from the transmitter coil.
The coupler element overlies a portion of both the transmitter and the receiver coils. Consequently, during energization of the transmitter coil and upon rotation of the coupler element, the inductive coupling between the transmitter coil and the first and second loops of the receiver coil is varied. This variable inductive coupling thus produces a voltage output from the receiver coil indicative of the angular position of the coupler element, and thus the position of the throttle pedal.
In order to obtain an accurate signal from these previously known throttle position sensors, it is important that the coupler element be concentric with the transmitter and receiver coils and also that the space between the coupler element and the transmitter and receiver coils remain constant throughout the entire movement of the coupler element. However, due to manufacturing tolerances in the manufacture of the throttle position sensor, the coupler element often is not precisely concentric with the transmitter and receiver coils and/or the space between the coupler element and the transmitter and receiver coils varies somewhat during pivotal movement of the coupler element. This lack of concentricity between the coupler element and the transmitter and receiver coils, as well as a variation in the spacing between the coupler element and the receiver and transmitter coils during rotation of the coupler element, will vary the inductive coupling between the transmitter coil and the first and second loops of the receiver coil and thus produce an output signal from the receiver coil different from a throttle position sensor with a precisely positioned coupler element at the same angular position.